1. Field of the Invention
This invention relates to disc brake assemblies for use in motor vehicles. More specifically, the present invention is directed to disc brake assemblies adapted to reduce the transmission of vibrations from the hydraulic brake system, especially those vibrations perceptible to a vehicle operator.
2. Disclosure Information
Disc brake assemblies of various designs are well known to the motor vehicle industry. Typically, disc brake assemblies include a caliper adapted to straddle a rotor and to support a pair of friction elements which are applied against opposite surfaces of the rotor to cause frictional braking. Generally one of the friction elements is mounted to a brake piston, or optionally to multiple brake pistons, which are disposed within cylinder bores formed in the caliper. Fluid pressure, generally hydraulic fluid pressure, is used to actuate the brake assembly by displacing the piston outwardly, thereby closing the gap between the friction elements and rotating rotor.
It is well known that surface irregularities in the rotor can cause vibration during vehicle braking. That is, as the working surface of the friction element is forced into contact with the surface of the rotor, the surface irregularities generate vibrations which travel through the friction element to the disc brake assembly. Especially during light to medium braking, the vibrations may be transmitted through the hydraulic system to create a tactile vibration at the brake pedal, steering wheel and floor perceptible by the vehicle operator. Such tactile braking vibrations are generally perceived adversely.
Remedial steps, such as turning the rotor to smooth its working surface, often are taken to reduce or eliminate the tactile vibrations. Also, various complex designs have been suggested for the brake piston for various purposes, some of which have included compliant members disposed between the brake piston and the friction element. One example of such a design is disclosed in UK patent application GB 2185547 of Osthoff et al., where an annular compliant member is interposed between a friction element and the brake piston, with curvature at the edges of the annular member to avoid friction between the piston and the brake shoe. The compliant members in these various prior arrangements, however, are subject to environmental deterioration and wear due to movement between the brake shoe and the brake piston. As the compliant member deteriorates, the tactile vibrations generated during vehicle braking are increasingly transmitted to the vehicle operator.
It would therefore be desirable to have a brake piston assembly having an environmentally protected internal compliant member for reducing the transmission of tactile vibrations to the vehicle operator during low and medium effort braking.